Urea-Formaldehyde (UF) resins are widely used as a binder for use in oriented strand board and particle board. These formaldehyde-based resins are inexpensive, colorless, and are able to cure fast to form a rigid polymer. Despite the effectiveness of the UF resins, particle board and oriented strand board often has a reputation for being of poor quality. Included in the quality is concern about the rate that these composites degrade when exposed to water or heat and humidity.
Another serious disadvantage of UF resin-bonded wood products is that they slowly emit formaldehyde into the surrounding environment. Formaldehyde is a know carcinogen and is part of a class of compounds that are commonly known as Volatile Organic Compounds (VOCs). Due to environmental, health, and regulatory issues related to formaldehyde emissions from wood products, there is a continuing need for alternative formaldehyde-free binders. Recent legislation has prohibited or severely restricted the use of formaldehyde in furniture and building materials in one or more states.
A number of formaldehyde-free compositions have been developed for use as a binder for making wood products. U.S. Pat. No. 4,395,504 discloses the use of formaldehyde-free adhesive system prepared by a reaction of a cyclic urea with glyoxal, for the manufacture of particleboard. Such a system, however, showed a rather slow cure and required acidic conditions (low pH) for the cure.
U.S. Pat. No. 5,059,488 shows an advantage of glutaraldehyde over glyoxal, when used in a reaction with cyclic urea. The patent discloses the use of glutaraldehyde-ethylene urea resins for wood panel manufacture. It was shown that this resin cured faster than glyoxal-ethylene urea resin, and the cure can be performed at a relatively high pH. However, the glutaraldehyde-based resins are not economically feasible.
U.S. Pat. No. 4,692,478 describes a formaldehyde-free binder for particleboard and plywood prepared of carbohydrate raw material such as whey, whey permeate, starch and sugars. The process comprises hydrolysis of the carbohydrate by a mineral acid, and then neutralizing the resin by ammonia. Although the raw materials are cheap and renewable, the reaction has to be performed at about 0.5. The pH makes handling difficult, dangerous, and costly.
U.S. Pat. No. 6,822,042 also discloses the use of a carbohydrate material (corn syrup) for preparing a non-expensive wood adhesive. Advantages of this binder include strong bonding, low cost, and renewable raw material. However, this adhesive requires the use of isocyanate as a cross-linker for this composition. Isocyanates are toxic making the use as a substitute for formaldehyde undesirable.
U.S. Pat. No. 6,599,455 describes a formaldehyde-free binder for producing particleboard containing curable thermoplastic co-polymers and cross-linkers selected from epoxy, isocyanate, N-methylol and ethylene carbonate compounds. Such compositions provide good strength and water resistance when cured. The epoxys are economically unfeasible do to the high material cost.
U.S. Pat. No. 6,348,530 describes a formaldehyde-free binder for producing shaped wood articles comprising a mixture of hydroxyalkylated polyamines and polycarboxylic acids. The binder preparation requires difficult steps to product and as a result is not economically viable.
One product that has emerged as a substitute for formaldehyde products is Purebond® proprietary manufacturing system for hardwood, plywoods and particle board. However, it is believed that Purebond® may include other toxic chemicals such as epichlorohydrin. While Purebond® is an improvement over the state of the art, it ultimately does not eliminate all dangerous or potentially dangerous compounds from its formulation. See http://www.columbiaforestproducts.com/products/prodpb.aspx.
See also U.S. Pat. No. 7,252,735. U.S. Pat. No. 7,345,136 (Heartland Resources Technologies) is believed to relate to H2H proprietary product, Soyad®. Soyad® is believed to include soy protein in a resin form, but does not eliminate the use of carcinogenic binders in combination with the soy protein.
Thus, after considerable attempts to solve the problem of urea formaldehyde adhesives, there exists a need to create a truly non-toxic high strength resin or composite system that does not contain any formaldehyde compositions or other carcinogenic compounds, is earth friendly and remarkably strong.
The state of the art is to find a resin that would be an effective replacement of formaldehyde resins. However, it would be desirable to provide a board that exceeds the current state of the art of particle board in strength. It would be further advantageous if this material was biodegradable, substantially, if not entirely from renewable sources, was environmentally friendly, and is stronger than state of the art particle board. It would be advantageous if the furniture boards had a thick, robust profile, but is surprisingly light weight. It is desirable that such curable compositions contain relatively high amount of non-volatiles, and at the same time are stable, fast-curing and do not emit any toxic fumes during the cure and afterwards. It would be desirable for the product to be not harmful to the environment when placed in a landfill. The present invention addresses one or more these and other needs.